Method for the differential flotation of sulphureted copper and zinc ores



Patented Mar. 13, 1934 PATENT OFFICE METHOD FOR THE DIFFERENTIAL FLOTA- TION ZINC ORES OF SULPHURETED COPPER AND Edmond Marie Camille Barthlemy, Brive-la-Gaillarde, France No Drawing. Application August 11, 1932,

Serial No. 628,448

6 Claims.

The invention relates to so-called flotation processes adapted to produce, by the wet'method, the enrichment or the separation of complex ores, and it more particularly refers to the separation of sulphureted copper ores from zinc blende, by differential flotation.

In'orde'r that the invention may be clearly understood the theory of flotation is indicated hereinafter.

The flotation phenomenon is a physical phenomenon which utilizes molecular surface actions. For carrying out a flotation process, three reagents are necessary, the functions of which are distinct:

(a) A froth producing reagent (pine oil, eucalyptus oil, creosote oil, etc.) which is adapted, by reducing the surface tension of water, to allow the air bubbles, artificially injected, to constitute fine bubbles forming a froth at the surface of the liquid.

(b) A collecting reagent (organic product such as xanthate for instance). This reagent preferably acts on the sulphides at the surface of which it is absorbed in a more or-less complex form, rendering this surface less easily wetted by water, so that the gaseous bubbles very easily adhere thereto. To this action is added an electronic action due to the fact that the gaseous bubbles are negatively charged, whereas the floatable sulphides are positively charged.

(0) A medium-modifying reagent (inorganic product such as lime, carbonate of sodium, acids, etc.) which, on the one hand, allow to obtain the optimum pH to the action of the collecting reagent, and, on the other-hand, can modify the electronic charges of the particles to be floated.

In differential flotation, a. depressing reagent for a sulphide will act on the surface of the particles of this sulphide by forming a surface which can be more easily wetted by water, therefore less adhering forthe air-bubbles, or it will modify the external charge of the particles by rendering it negative and, consequently, placing it in a condition allowing it to be driven back by the air bubbles.

A reactivating reagent will destroy the depressing fihn superficially formed on the particles of depressed sulphide.

Finally, certain bodies, such as zinc blende (zinc sulphide) are negatively charged so that their surface cannot be floated. They must be previously activated; for zinc blende the most powerful activating agentis any soluble -copper salt, unless the; blende is geoactivated, that is to say, unless it has been naturally activated by hydromineral circulations in the course of its formation, which is the case of blendes associated with copper ores. e

If the separation of galena and blende, by differential flotation, has been efliciently solved by the use of cyanide discovered by Sheridan and Griswold in 1922, the problem still remains difficult to solve if the ore contains copper, and particularly when it is desired to separate, by differential flotation, copper sulphides from blende.

The problem, in such cases, has always been connected with great difficulties arising from two main sources:

(a) Either, in the very midst of thedeposit, the

blende formed at the same time as copper sulsoluble copper salts to evolve, the effect of which has an activating actionon zincblende.

It is this latter phenomenon which is to be particularly considered when use is made of large quantities of cyanide. w

These general considerations have led the inventor to flrst seek, for the separation by differential flotation of zinc+'blende and copper sulphides, a depressing reagent specific of copper, in order to effect the .flotation of zinc blende. I

For improving the differential flotation of galena and blende in presence of copper sulphides, the inventor has sought for a reagent for disactivating blende, which has allowed him to carry out an improved method of differential flotation of copper and zinc by depression of zinc by means of cyanide.

supplementarylindications are given hereineach of the two methods.

I. Method by specific depression of copper mediately before flotation, or again by treatment of the ore in presence of the reagents or of one of thereagents at a temperature lower than the temperature of roasting of the sulphides before flotation.

.Zinc blende is then floated first, according to the classical process, by utilizing a collecting agent other than xanthate of potassium, for instance by means of diethyl dithiophosphate of sodium, after suitable activation.

After zinc blende has been floated, the copper sulphides will be floated in their turn, by means of xanthate, by alkalizing the circuit to a suitable degree.

This method, which has been applied to a series of ores of various origins and containing a very wide range of more or less complex copper sulphides (enargite, tennantite, tetrahedrite, etc.), is described hereinafter.

(a) The action of ferrocyanide or ferricyanide on copper sulphides is very powerful owing to the formation of a film of CUiZFGCYB which can be clearly seen with a microscope. This action takes place at ordinary temperature, but is highly activated by slight heating.

Depression of copper sulphides by ferro or ferricyanides:

The ferrohydrocyanic ion or ferrihydrocyanic ion is absorbed in a few minutes by the crystalline faces of copper sulphides, forming a complex ion on which the collecting reagent of zinc blende (diethyl dithiophosphate of sodium) does not act.

Zinc blende alone is then placed in condition to be floated and as consequence floats, while the copper sulphides do not float.

The action of carbonate has for effect to establish the optimum pH to the action of ferrocyanide or ferrlcyanide, and at the same time to facilitate this action.

The xanthate ion which destroys the complex film formed at the surface ofthe copper sulphides by the ferrocyanide or ferricyanide then acts on the copper sulphides as collecting agent.

From this theory it results that any collecting body which does not destroy the complex depressing ion formed at the surface of the copper sulphides can be used in the process as collecting agent for zinc blende (for instance diethyl dithiophosphate of sodium).

After flotation of the blende, any body destroying this complex ion will reactivate the copper, that is to say will place it in condition to be floated after addition of a collecting agent. For instance xanthate, which-reactivates the copper, being also ejcollecting agent, fulfils both functions.

aluminium acetate or sulphate, action.

Free acids destroy the depressing film of copper and, consequently, are prejudicious to the said action. A

(b) Flotation of zinc blenda-Since flotation of zinc blende is to be first effected, it is necessary to completely avoid the use of xanthate as collecting agent for the same, since it reactivates copper.

The collecting agent which has given the inventor the best results for floating zinc has been diethyl dithiophosphate of sodium which is a product marketed by the American Cyanamid Co. of New York.

Interesting results have also been obtained with the reagent No. 208 produced by the same firm.

The TT classical reagent can also be used (solution of thiocarbanalid of 20% strength in orthotoluidine). Diphenylguanidine and diorthotolylguanidine, as well as the combination of the first of these bodies with mercaptobenzothiazole, constitute collecting agents which can be conveniently employed.

(0) Reactivation of copper.-Xanthates have proved to be the best reactivating agents of copper, probably owing to the fact that ferro and ferricyanides of copper are destroyed by these promotes this reagents and converted into xanthates of cop-' per. Xanthates, which are already excellent collecting reagents for sulphides, are therefore alone sufilclent for floating copper sulphides after zinc blende has been removed by a first flotation.

Influence of the gangues.-Most of the gangues usually have a prejudicious action owing to the facility with which they absorb ferrocyanide. It will therefore often be necessary to efiect a first flotation with the collecting agent of the blende, which flotation will carry away an appreciable quantity of copper sulphides. The method is thereupon again applied on the concentrate obtained, in order to have a satisfactory result.

Compound flotation products and refractory ores.--As in any differential flotation, there is no very distinct point corresponding to the end of the flotation of zinc blende. After having obtained a concentrate which is very rich in zinc and having a low content of copper, and by continuing the flotation, a compound product still containing zinc but already a high proportion of copper, will be obtained.

This product will then be subjected to another treatment in order to eflect on the said product a better separation. Usually, another simple treatment with addition of ferrocyanide (second flotation) will be sufiicient.

Sometimes, on the contrary, the agglomeration of the grains of zinc blende and copper sulphides is such that a more vigorous treatment is necessary. The compound products resulting from a first flotation will then be dried, and subsequently heated with ferrocyanide and carbonate during about one hour, between 270 and 350 C. The higher temperature will, in any ucts might begin.

After this heating, the products will be converted into pulp and floated according to the steps oi the process.

This method has'an extremely powerful action and can be very conveniently applied, in the case of refractory ores, to the normal method of procedure. However, since it is almost impossible to float copper after such depression in the hot state, the method must always be applied to a product free from gangue, so that after flotation of zinc, the nonfloated residue may constitute the copper concentrate.

Practical results.To exemplify the method, a typical result of application of the process is given hereinafter:

Ore B. P. U. 4?.On analysis, this ore is composed as follows:

Zinc 16.02% Copper 13.84% Iron 7.08% Sulphur 16.30%

From the mineralogic standpoint, the copper is approximately distributed as follows:

62% in the form of bornite, 23% in the form of chalcopyrite,

10% in the form of chalcosine, 5% in the form of covelline.

This ore has been crushed up to 64%'passing through a 200 mesh sieve, in-a ball crusher with:

300 grs. of ferrocyanide of sodium and 1500 grs. of carbonate of sodium per ton of ore treated.

The flotation has been effected in pulp form with 30% of solids, and with a pH value of 8.3.

The flotation of zinc has been eifected with (per ton of ore) 400 grs. of crystallized S04Cu, 150 grs. of diethyl dithiophosphate of sodium, and grs. of essential oil of eucalyptus.

For 1000 grs. of ore treated, 202 grs. of zinc concentrate have been recovered, the analysis of which is the following:

Zn:58.92% with:Cu 4.4%

this corresponding to a recovery of 74.5% of zinc with 6.7% of copper carried along.

Near the end, 40 grs. of a compound product have been separated which, on analysis, was composed as follows:

Zn:36.7% and Cu 22.8%

this representing 9.06% of the zinc and 6.5% of the copper.

Flotation of copper has then been effected by means of an addition of 200 grs. of xanthate of potassium per ton of ore treated. This flotation has given 261 grs. of, a copper concentrate, composed as follows:

Cu 44.0% with Zn 8.05%

that is to say a recovery of 83% of the copper containing only 13.1% of the zinc.

The residue of the flotation: about 500 grs., is composed as follows:

Cu 1.01% and Zn 1.12%

after addition of 1000 grs. of crystallized copper sulphate per ton of product and 125 grs. of diethyl dithiophosphate of sodium, and 45 grs. o1 eucalyptus oil. L

The flotation has I given a product composed as follows:

representing 46% by weight of the products subjected to this flotation, so that the zinc concentrate thus obtained contains: 73.6% of the zinc and carries along 16.3% of the copper.

The residue of flotation constitutes acopper concentrate, composed as follows? Cu 35.3% with Zn 18.0% Thus, by combining these latter concentrates,

"according to their proportions, with the concentrates of the original operation, it is possible, with the methods according to the invention, to obtain:

Ore treated Cu 13.84%-Zn 16.02% Zinc concentrate Cu. 4.88%-Zn 58.80% Copper concentrate Cu 43.30%-Zn 8.78% Residue; Cu 1.01%Zn 1.12%

II. Method by disactivation of zinc blende In a second method, also included in the scope of the invention, the reverse mode of procedure is adopted, that is to say suitable depression of zinc blende is produced, the copper sulphides being then floated first.

The classical method, by means of cyanide, for depressing zinc blende in a flotation is practically defective when the ore treated contains copper ores. In fact, copper cyanide is then formed, which, as all soluble copper salts, is an activating agent for zinc blende. In these conditions, the depressing action of alkali cyanides on zinc blende is compensated by the activating action of the copper cyanide formed.

By means of the invention, it is possible to obtain a'suitable depression of zinc blende by alkali cyanides, by preventing any formation of copper cyanide. For that purpose, with cyanide is added a metallic powder capable of separating copper from its soluble salts.

Use will, for instance, preferably be made of zinc powder. The latter is particularly convenient in that it causes the formation of a zinc salt, which is itself a depressing agent for zinc blende.

This second method can also be used with the same success for diflerential flotation of ores containing galena and zinc blende with traces of copper ores. Diflerential flotation of such ores has been considered up to now as presenting great difliculties, as zinc blende is then depressed with dimculty and in fact is never completely depressed.

According to the invention, depression of the zinc sulphide is promoted in these ores by addition of zinc powder. The use of ferrocyanide is,

in this case, also useful for disactivating zinc blende.

Supplementary informations are given hereinafter concerning the application of this method.

v It is recognized that activation of zinc blende, that is to say placing it in condition to be suitably floated by means of the usual collecting agents, necessitates the action of a copper salt which will form on the crystalline faces of zinc blende a monomolecular film of CuS, 3ZnS.

This activation which, in generaLis artificially obtained by means of copper sulphate, can be natural'in the case of geoactivated blendes, as explained at the beginning of this specification.

Any reagent which will destroy this film of cyanide in the pulp, then causing the flotation copper sulphide will therefore act for promoting depression of zinc blende.

Researches have then been made concerning the use of finely divided metals capable of precipitating copper from its salts. A series of metallic p0wders.have then been tried by the inventor, but the researches have rapidly been limited to the folowing metallic powders:

Mg, Al, Zn, Sn, have proved to be distinctly more active than those of other metals.

At the commercial standpoint, zinc is to be preferred, considering the ease with which it can be used and its low price even for an extremely fine product (98% passing through a 200 mesh sieve).

Magnesium is very active but its use is relatively dangerous.

Zinc also gives satisfactory results and its action appears to be but very slightly affected by the condition of hydrolysis and ionization of the pulp.

Experiments have also been effected with sea water; the results obtained on various ores have also been satisfactory, and sometimes even better than with ordinary water.

Moreover, the use, with zinc, of ferrous salts (preferably chloride), often renders the disactivating action of blendes extremely powerful.

Thus, the treatment, in the form of finely crushed pulp, of an ore containing geoactivated blendes with metallic zinc in powder form has for effect to disactivate these blendes, thus rendering them capable of being depressed by means of cyanide by the Sheridan and Griswold method.

Metallic zinc also avoids the formation of soluble copper cyanides which might again activate zinc blende.

I claim: a r

1. A method for separating sulphide copper cres from zinc blende by differential flotation,

which consists in converting the ore into pulp, giving the pulp an alkalinity, adding before flotation an alkali ferro-cyanide which can produce a colloidal copper ferro-cyanide in the pulp, then causing the flotation of zinc blende in the presence of a collecting agent of the dithiophosphate type, which broadly has no destructive chemical action on colloidal copper ferro-cyanide, then causing the flotation of the copper sulphides in the presence of a collecting agent of the xanthate type which broadly has a destructive chemical action'onc olloidal copper ferro-cyanide.

2. A method for separating sulphide copper ores from zinc blende by differential flotation, which consists in converting the ore into pulp, giving the pulp an alkalinity, then forming in the pulp before flotation an alkali 'ferro-cyanide which can produce a colloidal copper ferroof zinc blende in the presence of a collecting agent of the dithiophosphate type which broadly.

- has no destructive chemical action on colloidal of the copper sulphides in the presence of a collecting agent of the xanthate type which broadly has a destructive chemical action on colloidal copper ferro-cyanide.

3. A method for separating sulphide copper ores from zinc blende by differential flotation, which consists in treating the ore in the presence of an alkali ferro-cyanide at a temperature lower than the roasting temperature of the sulphides and converting the ore into pulp, giving the pulp an alkalinity, thereupon causing the flotation of zinc blende in the presence of a collecting agent of the dithiophosphate type, which broadly has no destructive chemical action on colloidal copper ferro-cyanide, then causing the flotation of the copper sulphides in the presence of a collecting agent of the xanthate type which broadly has a destructive chemical action on colloidal copper ferro-cyanide.

4. A method for separating sulphide copper ores from zinc blende by differential flotation, which consists in converting the ore into pulp, giving the pulp an alkalinity, adding in presence of aluminium salts before flotation an alkali ferro-cyanide which can produce a colloidal copper ferro-cyanide in the pulp, then causing the flotation of zinc blende in the presence of a collecting agent of the'dithiophosphate type, which broadly has no destructive chemical action on colloidal copper ferro-cyanide, then causing the flotation of the copper sulphides in the presence of a collecting agent of the xanthate type which has a destructive chemical action on colloidal copper ferro-cyanide.

5. A method for separating sulphide copper ores from zinc blende by differential flotation, which consists in converting the ore into pulp, giving the pulp an alkalinity, then forming in the pulp in the presence of aluminium salts before flotation an alkali ferro-cyanide which can produce a colloidal copper ferro-cyanide in the pulp, then causing the flotation of zinc blende in the presence of a collecting agent of the dithiophosphate type which broadlyhas no destructive chemical action on colloidal copper ferro-cyanide, then causing the flotation of the copper sulphides in the presence of a collecting agent of the xanthate type which broadlyhas a destructive chemical action on colloidal copper ferro-cyanide.

6. A method of separating sulphide copper EDMOND MARIE CAMIILE BARTHELEMY. 

